The objective of the proposed research is to further define the kidney's role in regulating salt and water balance. Evaluation will be in terms of 1) the importance of prostaglandins and angiotensin in regulating pressure-volume characteristics of the interstitial space in normal and hypertensive animals and 2) identification of the nephron site responsible for the natriuresis following release of a renal artery constriction. Studies will be performed utilizing body fluid space measurements and micropuncture techniques in the rabbit.